1. Technical Field
The present disclosure relates generally to electrosurgical systems. In particular, the present disclosure relates to universal safety electrosurgical return electrodes that are adapted to be used with patients of substantially any size.
2. The Relevant Technology
In the area of electrosurgery, medical procedures of cutting tissue and/or cauterizing leaking blood vessels are performed by utilizing radio frequency (RF) electrical energy. As is known to those skilled in the medical arts, electrosurgery is widely used and offers many advantages including that of the use of a single surgical tool for both cutting and coagulation. The RF energy is produced by a wave generator and transmitted to a patient's tissue through a hand-held electrode that is operated by a surgeon.
Every monopolar electrosurgical generator system must have an active electrode that is applied by the surgeon to the patient at the surgical site to perform surgery and a return path from the patient back to the generator. The active electrode at the point of contact with the patient must be small in size to produce a high current density in order to produce a surgical effect of cutting or coagulating tissue. The return electrode, which carries the same current as the active electrode, must be large enough in effective surface area at the point of communication with the patient such that a low density current flows from the patient to the return electrode. If a relatively high current density is produced at the return electrode, the temperature of the patient's skin and tissue will rise in this area and can result in an undesirable patient burn. According to the Emergency Care Research Institute, a well-known medical testing agency, the heating of body tissue to the threshold of necrosis occurs when the current density exceeds 100 milliamperes per square centimeter. Furthermore, the International Electrotechnical Commission (“IEC”) has published standards that require that the maximum patient surface tissue temperature adjacent an electrosurgical return electrode shall not rise more than six degrees)(6° Celsius under stated test conditions.
Since the inception of electrosurgery, various types of return electrodes have been used. Initially, return electrodes consisted of flat stainless steel plates (which in later years were coated with a conductive gel) that were placed under the patient's buttocks, thigh, shoulders, or any location where gravity could ensure adequate contact area. Due to adjustments during a procedure, however, the contact area between the patient and the steel plate sometimes dropped below adequate levels. In such instances, the density of the current being transferred from the patient to the steel plate sometimes increased to levels that resulted in the patients being burned.
In an effort to improve the safety of return electrodes, the flat steel plates were eventually replaced with flexible return electrodes. Like the steel plate electrodes, the flexible return electrodes are also coated with a conductive or dielectric polymer. Additionally, the flexible return electrodes have an adhesive border on them so they can be attached to the patient without the aid of gravity. Because these flexible return electrodes are attached to the patients with an adhesive, these types of return electrodes are often referred to as “sticky pads.” Upon completion of the electrosurgical procedure, these sticky pads are disposed of. Expectedly, the disposable nature of sticky pads has resulted in additional surgical costs in the United States of several tens of millions of dollars each year.
The use of sticky pads has resulted in fewer patient return electrode burns compared to the old steel plates. Nevertheless, hospitals are still experiencing some patient burns caused by sticky pads that accidentally fall off or partially separate from the patient during surgery. Furthermore, in order to achieve the reduced number of patient burns, the size and shape of the sticky pads have to match the available surface area of the patient.
For instance, if an adult sized sticky pad were used on a baby, parts of the sticky pad would not be in contact with the baby. As a result, the current density through the portion of the sticky pad that is in contact with the baby may increase to levels that cause burns on the baby. Additionally, the unattached portions of the sticky pad could also pose a burn risk to operating room personnel.
Additionally, due to the smaller surface areas of the sticky pads, the power settings on the generators must be limited to control/limit the current density being transferred through the sticky pads. As a result, for instance, an infant sized sticky pad cannot be used on an adult patient because the required power settings to achieve the desired surgical effect cannot be used without the risk of causing a sticky pad site burn due to the small surface area.
In further attempts to alleviate the foregoing issues, standards (IEC 60601-2-25th Edition) have been established that divide patients in three weight ranges: less than 5 kg, 5 kg to 15 kg, and over 15 kg. Sticky pads have been made specifically sized to accommodate each weight range. Additionally, power setting limits have been established for sticky pads used in each weight range. Specifically, the IEC standards require that the electrosurgical current used with the sticky pads for the less than 5 kg weight category not exceed 350 milliamperes (“mA”). Similarly, the IEC standards require that the electrosurgical current used with the sticky pads for the 5 kg to 15 kg and the over 15 kg weight categories not exceed 500 mA and 700 mA, respectively.
Subsequently, there was proposed a further improvement, an Electrode Contact Quality Monitoring System that would monitor the contact area of the electrode that is in contact with the patient and turn off the electrosurgical generator whenever there was insufficient contact area. Such circuits are shown, for example, in U.S. Pat. No. 4,231,372, issued to Newton, and entitled “Safety Monitoring Circuit for Electrosurgical Unit,” the disclosure of which is incorporated by this reference. This system has resulted in additional reduction in patient return electrode burns, but requires a special disposable electrode and an added circuit in the generator that drives the cost per procedure even higher. Additionally, these types of monitoring systems only provide a relative amount of safety. More specifically, such monitoring systems are controlled by human generated algorithms. In creating such algorithms, the algorithm creator must decide what parameters (e.g., contact area size, etc.) are considered safe. In use, however, the selected parameters may prove not to provide sufficient safety. Thus, the safety of such monitoring systems is only as good as the parameters selected for the algorithm in the monitoring system. In the first twenty years after this system was introduced, fewer than 40 percent of all the surgical operations performed in the United States used this system because of its high costs.
One of the biggest improvements to electrosurgery came in the form of self-limiting return electrodes. Unlike sticky pads and steel plate return electrodes, self-limiting return electrodes are relatively large, thereby eliminating the need for conductive gels that may irritate a patient's skin. Additionally, self-limiting return electrodes typically employ geometries and materials whose impedance characteristics, at typically used electrosurgical frequencies, are such that the return electrode self-limits current densities (and corresponding temperature rises) to safe thresholds, should the contact area between the patient and the electrode be reduced below otherwise desirable levels. Furthermore, self-limiting return electrodes were specifically designed to evenly distribute the current density over the entire contact area between the patient and the return electrode. The even distribution of the current density was intended to further reduce the risk of patient burns.
While the use of self-limiting return electrodes has even more dramatically reduced the number of patient burns experienced during electrosurgical procedures, typical self-limiting return electrodes still suffer from some limitations. For instance, like sticky pads, typical self-limiting return electrodes are commonly made in multiple sizes for different sized patients. For instance, a typical self-limiting return electrode for a relatively small person (e.g., under 50 lbs) may be about 26×12 inches while a typical self-limiting return electrode for a larger person may be about 46×20 inches.
Furthermore, typical self-limiting return electrodes are often asymmetrical in their construction such that only one surface of the electrode can be used as a working surface. As a result, operating room personnel must take care to ensure that the return electrode is positioned on the operating room table with the proper surface facing upward toward the patient. If the working surface is not positioned towards the patient, there may be insufficient capacitive coupling between the patient and the return electrode for the return electrode to function properly.
The asymmetrical nature of the construction is often due to the inclusion of additional or thicker layers of materials (e.g., dielectric, cushioning, etc.) on one side of a conductive element than on another side. Not only does the asymmetrical construction of typical self-limiting return electrodes limit which surfaces can be used as working surfaces, but the thickness of some of the layers can limit the ability of the return electrode to work across different categories of patients. For instance, a self-limiting return electrode that works for an adult may not provide sufficient coupling for an infant because a cushion layer is too thick.
Thus, although various advances have been made in the electrosurgical arts, there remains room for improvement. More particularly, while systems and devices have been developed to increase the safety of patients undergoing electrosurgical procedures, such as by reducing the number of patient return electrode burns, the versatility of return electrodes has remained an issue. In particular, as noted above, previous return electrodes have needed to be tailored to different categories of patients (typically size categories) and have been limited in the particular manner of use (e.g., current levels, orientation of working surface, etc.).
Therefore, it would be an advance in the present electrosurgical art to provide a universal safety electrosurgical return electrode that is self-limiting and that can be used across all categories of patients and in more versatile ways.